Autonomous vehicles, also referred to as self-driving cars, navigate autonomously through an environment with minimal or no human input. To navigate autonomously, a vehicle determines a location within an environment so that various obstacles can be avoided and to ensure that the vehicle remains on the roadway. In general, autonomous vehicles may use various sensors including, for example, cameras to help the vehicle detect and identify obstacles in the environment. Thus, by way of example, the vehicle can use the cameras to obtain images of the roadway and identify lane markers within the images. As a result, the vehicle can, for example, determine whether it is presently within and keeping a particular lane in relation to the lane markers.
However, identifying the lane markers in the described manner can present difficulties when, for example, precipitation (e.g., rain, snow, ice) is present on the roadway, when markers become worn, when visibility is poor (e.g., fog, snow), when a clear view is occluded by traffic, and so on. Moreover, identifying the lane markers as described provides information about the lane markers themselves, but does not provide additional information about the roadway or the surrounding environment.